The invention relates to the general field of telecommunications, and more particularly it concerns a novel architecture for an Internet protocol (IP) core network.
A preferred but non-limiting application of the invention thus lies in the work currently being undertaken by the 3GPP standard to define the evolved packet core (EPC) network for use within the evolved packet system (EPS) architecture as proposed by the consortium.
Over the last few years, there has been unprecedented increase in mobile telecommunications traffic, spurred on by the appearance of new mobile applications, new terminals, and ever higher communication data rates. Conversely, a recent study emphasizes that the revenues of operators are decreasing exponentially in spite of the increase in traffic, with the costs of developing and operating networks being at the point of exceeding the revenues generated by using them. This can be explained in part by the fact that present network architectures are rather poorly adapted to satisfying this dual problem of high demand in terms of traffic while also remaining a source of revenue for operators.
In this context, the evolved packet system (EPS) architecture was defined by the 3GPP consortium to provide IP connectivity between a user terminal and external packet data networks (PDNs), capable of providing the terminal with various communications services, such as voice over IP (VoIP) services, data downloading, videos on demand, etc. Such an external data packet network may for example be the Internet public network or a data center. That architecture is presently under rapid development. Specifically, these expected traffic models change very dynamically and often unpredictably, such that new technical and financial constraints are placed on the operators of telecommunications networks.
One of the major stakes in the EPS architecture, and more particularly in the evolved packet core (EPC) network on which that architecture relies, is to provide an IP connectivity service on demand. This service relies on communications sessions being handed over in a manner that is temporary and transparent for the user from one piece of equipment to another within a single access network or from one access network to another. The term “transparent” is used to mean that the transfer must be capable of taking place without interrupting the user's communications sessions and while minimizing any loss of data packets exchanged during those sessions. This constraint is particularly critical at present in situations where it is envisaged that a terminal might be mobile between access points of a given non-licensed access network, such as for example a wide local area network (WLAN), or between a non-licensed access network to a licensed access network, such as a 3GPP access network.
The term “licensed” network is used herein to mean an access network that uses a frequency spectrum that is subjected to utilization licenses, such as for example the 2G/3G/4G network or indeed the 5G network. In contrast, “non-licensed” access networks make use of frequencies that are freely available. By way of example, one such network is a WLAN or a WiFi network.
FIG. 1 shows the EPC network architecture as presently envisaged by the 3GPP standard, together with the various pieces of equipment on which it relies. By way of indication, provision for exchanges between those pieces of equipment for the purpose of transferring data (i.e. in the data plane or user plane) are represented by continuous lines, whereas provisions for exchanges of signaling between those pieces of equipment in order to support such transfers of data (i.e. in the control or signaling plane) are represented by dashed lines.
In the example shown in FIG. 1, an access point 1A of a non-3GPP access network is connected to an evolved packet data gateway (ePDG) 2 via a communications interface using a communications tunnel set up using the Internet protocol security (IPsec). The ePDG gateway 2 is connected via an S2a/S2b communications interface to a PDN gateway (PGW) 3 for interconnection with an external packet data network 4. The S2a/S2b communications interface relies on setting up a communications tunnel using the GPRS tunneling protocol (GTP) communications protocol or using the proxy mobile IP protocol (PMIP). The PGW gateway 3 and the external network 4 are connected together via an SGi communications interface.
In that architecture, a base station 5 of a 3GPP access network (e.g. an LTE or eUTRAN access network) is connected to a serving gateway (SGW) data transfer gateway 6 via an S1-U communications interface, and to equipment 7 for managing terminal mobility known as a mobile management entity (MME) via an S1-MME communications interface.
The SGW gateway 6 is connected to the PGW gateway 3 via an S5 communications interface (comprising S5-U signaling supporting exchanges of data in the user plane and S5-C signaling supporting exchanges of data in the control plane). This S5 communications interface also relies on the GTP communications protocol. The SGW gateway 6 is also connected to the MME equipment 7 via an S11 communications interface.
The MME equipment 7 is in charge of providing IP connectivity for terminals when they are in a situation of mobility within the 3GPP access network. It is connected via an S6a communications interface to a user database 8 also known as the home subscriber server (HSS).
In this context, consideration is given to a user connected via a terminal to the non-3GPP access network via the access point 1A. This user is participating in one or more communications sessions set up between the access point 1A and the PGW gateway 3 for interconnection with the external network 4, and passing via the ePDG gateway 2.
In the architecture as set out at present by the 3GPP consortium and as shown in FIG. 1, if the terminal discovers a new access point 1B of the non-3GPP access network and connects to the new access point, all of the active sessions of the terminal as set up via the access point 1A are interrupted, and need to be set up again, and this applies regardless of whether the access point 1B is or is not connected to the same ePDG gateway 2 as the access point 1A. The same applies when the terminal connects to another access network, and in particular to a base station 5 of the 3GPP access network.
These interruptions of the communications sessions of the terminal result firstly in a poor quality of experience (QoE) for the user of the terminal, and secondly to a large amount of signaling on the network in order to set the sessions up again, which can lead to a period of temporary congestion in the network.
The EPC architecture as presently designed gives little or no flexibility for mitigating these difficulties and for offering an on-demand IP connectivity service. Specifically, the various above-described pieces of equipment of the EPC architecture, and in particular the MME equipment 7, the SGW gateway 6, the PGW gateway 3, the ePDG gateway 2, and the HSS subscriber server 8 are provided by hardware that is deployed, provisioned, and configured in a manner that is static, so it is difficult to change any behavior. Furthermore, those pieces of equipment present close coupling firstly between hardware and software aspects, and secondly between the user plane and the control (or signaling) plane, which cannot be modified dynamically, and thus provide no flexibility.
Consequently, there exists a need for an IP core network architecture that does not present such drawbacks and that makes it possible to provide an on-demand IP connectivity service to users with a quality of experience that matches their needs and their expectations.